Transponder communication device for the contactless communication with a plurality of individually selectable transponders, and transponder for the contactless communication with at least one transponder communication device.
The invention relates to a transponder communication device adapted to provide contactless communication with a plurality of individually selectable transponders, including transponder selection means for the successive individual selection of transponders present within a receiving range of the transponder communication device and which are each in an active state interrogation means, included in the transponder selection means, for generating at least one item of interrogation information by means of which transponders present within the receiving range and which are each in their active state can be interrogated to generate and transmit answer information, and transmission means for transmitting the at least one item of interrogation information to transponders present within the receiving range, and receiving means for receiving answer information generated and transmitted by transponders present within the receiving range in response to the at least one item of interrogation information, and deactivation means, included in the transponder selection means, for generating at least one item of deactivation information by means of which a transponder present within the receiving range, and which is in its active state upon its selection, can be set to a state in which the transponder does not generate and transmit answer information in response to the at least one item of interrogation information.
The invention further relates to a transponder adapted to provide contactless communication with at least one transponder communication device and adapted to be selected, when it is in an active state, by a transponder communication device, including receiving means for receiving at least one item of interrogation information transmitted by a transponder communication device, and interrogation detection means for detecting at least one item of received interrogation information, and answer means adapted to be controlled by the interrogation detection means to generate answer information in response to received interrogation information detected by the interrogation detection means, and transmission means for transmitting the answer information generated by the answer means, and deactivation means by means of which the transponder can be set to a state in which the transponder does not generate and transmit answer information in response to interrogation information.
A transponder communication device of the type defined in the first paragraph and a transponder of the type defined in the second paragraph are commercially available and are consequently known. For such a known transponder communication device as well as for such a known transponder reference can be made, for example, to the document U.S. Pat. No. 5,345,231 A.
With regard to a known transponder communication device and to a known transponder the afore-mentioned document U.S. Pat. No. 5,345,231 A expounds that in the case that a plurality of known transponders are present within the receiving range of a known transponder communication device the problem of the individual selection of each of the individual known transponders arises. This individual selection can be effected with the aid of selection means of a known transponder communication device, which for this purpose include interrogation means capable of generating and transmitting at least one item of interrogation information and by means of which each of the transponders present within the receiving range of a known transponder communication device can be requested successively to generate and transmit answer information to the known transponder communication device. In the known transponder communication device the presence of a plurality of transponders present which are each in an active state is detected by means of a presence protocol, the transponder communication device starting an interrogation, after detection of a plurality of transponders present within the receiving range of the transponder communication device, whether one transponder among one half of the total number of transponders is present within the receiving range of the transponder communication device. This is effected in that the transponder communication device transmits an interrogation protocol. If one or more transponders of the interrogated half of the total number of transponders are present within the receiving range of the transponder communication device, these transponders, which are each in the active state, respond by transmitting their individual codes and some test bits to the transponder communication device. Each individual code then forms answer information which is generated in the relevant transponder and is transmitted by the relevant transponder. If a transponder responds, the transponder thus has already been selected. However, if several transponders respond, this will result in a superposition of answer information, which in conjunction with the test bits is detected in the transponder communication device. Subsequently, the transponder communication device starts a further interrogation, said half of the total number of transponders being halved again. This process is repeated until only one transponder responds. If no transponder responds to an interrogation, the process proceeds with the division of the complementary transponder group. When a transponder has been selected, its re-selection during a subsequent selection process is inhibited in that deactivation means provided in the transponder communication device generate deactivation information by means of which, after its selection, a transponder present within the receiving range can be set from its active state into a state in which it does not generate and transmit any answer information in response to interrogation information, thus assuring that a transponder already selected can be re-selected only after all the other transponders present within the receiving range of the transponder communication device have been selected.
In a known transponder communication device and a known transponder the problem occurs that in practice the division of the total number of transponders capable of communicating with the known transponder communication device into groups which are each time halved requires comparatively much time, because the selection of a transponder requires up to .sup.2 logX divisions and, consequently, interrogations, X being the total number of transponders capable of communicating with the transponder communication device rather than the number of transponders actually present within the receiving range of the transponder communication device. Therefore, if a comparatively large number of transponders are at the same time present within the receiving range of the transponder communication device, the individual selection of all the transponders present within the receiving range can take a comparatively long period of time, for example when the transponder communication device and the transponders for the contactless communication with this device form parts of a road toll system, in which each transponder is on board of a motor vehicle and the transponder communication device is situated at the location of a stationary toll station.